Carbon brush assembly



Oct. 13,- 1970 J. J. CAREY 3,534,206

' I CARBON BRUSH ASSEMBLY Filed Ochs). 1969 F/6.4 YH65 1 NVEN TOR. /4/Vf4 54425 Y 4rrofeA/e; Y

United States Patent O 3,534,206 CARBON BRUSH ASSEMBLY James J. Carey, Park Forest, lll., assignor to The Carbone Corporation, Boonton, NJ., a corporation of New Jersey Filed Oct. 9, 1969, Ser. No. 865,135 Int. Cl. H02k 13/00 U.S. Cl. 310-247 8 Claims ABSTRACT OF THE DISCLOSURE A carbon brush assembly for electrical motors in which a current carrying metal plate is secured to the end of the brush and an electrical conductor secured to the plate. A spring presses against the plate but is not designed to carry current. The metal plate is secured to the carbon brush by means of a cylindrical extension, formed integral with the plate, which is press-fitted into a hole in the brush.

BACKGROUND OF THE INVENTION The use of carbon and graphite brushes to serve as a sliding contact with moving parts of electrical machinery is well known. Brushes of this type require a resilient mounting to allow for slight radial motion as a commutator or slip ring revolves and to keep thebrush in constant contact as the brush material wears away. Prior art brush assemblies have used a helical spring for keeping the brush pressed against the rotating conductor and also for carrying the current. Most springs have high resistance which results in a loss of energy and also generates considerable heat. On heavy loads, the heat generated may be suicient to destroy the spring temper and require replacement.

The present invention uses a metal plate between the br-ush end of the spring and the brush. The current is applied to the plate by a ilexible conductor and the spring carries no current. Such arrangements are known in the art but have been lacking in good conduction because there have been no satisfactory means of securing the plate to the brush to create a low resistance union. In the present invention the pltae is formed with an extension which is forced into an axial hole in the brush. This type of contact means has been found to have substantially no resistance and, in addition, it possesses a flat top surface for the application of any type of simple spring.

One of the features of the invention is the ease in which the brush and conductor may be assembled or replaced in a small machine. It is not necessary to remove the moving commutator or slip ring when a change of brushes is being made.

For a better understanding of the present invention, together with other details and features thereof, reference is made to the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a cross sectional view of one form of the invention showing the brush, the contact plate, and the spring inside a brush holder.

FIG. 2 is a cross sectional view of the brush assembly shown in FIG. 1 and is taken along line 2 2 of that ligure.

FIG. 3 is a bottom view of the conductive metal plate.

FIG. 4 is a bottom view of an alternate form of metal plate having an extension with a corrugated cylindrical surface.

FIG. 5 is an isometric view of another form of metal 3,534,205 Patented Oct. 13., 1970 ICC plate having a plurality of spring teeth secured to its under side instead of the cylindrical extension.

DESCRIPTION OF THE PREFERRED EMBODIMENT The brush assembly includes a cylindrical holder 10 closed by a cap 11 which may be threaded to the holder or retained by other means. The holder 10 and cap 11 are shown as made of metal in the drawings but, if desired, they may be made of nonconductive materials. A brush 12 is positioned in the holder 10 with its lower surface resting on a rotatable member 13 which may be a commutator, a slip ring, or any other moving part which derives current from the brush 12.

The brush 12 is formed with an axial hole 14 at its upper end for receiving an extension 15, formed integral with a disc type plate 1'6. The lower end of the brush makes contact with the rotatable member 13 for the transfer of electrical current. The plate 16 includes an annular at portion which rests on top of the brush 12 and also forms a contact area for a helical expansion spring 17. The other end of the spring 17 is held in position by the inside surface 18 of cap 11.

Plate 16 also carries the end of a flexible conductor 20 which is secured to the edge of the plate by crimping or by welding. As shown in the figures, the edge of plate 16 is turned over at 21, securing a circular portion of the flexible conductor 20. It is obvious from the gures that the only current path is from the conductor 20 to the pltae 16, then to the brush 12, and the rotary member 13. Neither the springs 17 nor the holder 10 is required to carry current.

The construction shown in FIG. 1 permits the brushes 12 to be assembled without removing the rotary member 13. The cap 11 is removed and the brush assembly, including the plate 1-6 and conductor 20, is inserted into the holder 10 with the conductor 20 positioned in slot 22. Slot 22 is open at the cap end of the holder but it can be cut from the other end. In the lattter case, a threaded cap 11 is not necessary but then assembly must be made through the lower end which requires the removal of the rotary member 13 or the removal of holder 10.

The extension 15 on plate 16 is designed to be presstted into hole 14 in the upper end of brush 12. A more substantial contact can be made if the extension is formed with small corrugations (see 15A in FIG. 4). When this extension is pushed into hole 14, some of the brush material may be removed from the side of the hole but the contact is better and the corugations prevent relative rotation.

FIG. 5 shows another alternate arrangement of the contact plate. Contact plate 16A is flat but has a plurality of downwardly extending spring times 23 which resiliently engage the side of hole 14 in the brush. The flexible conductor 20 may be crimped to the edge of the plate as described in connection with FIGS. 1 and 2. but connection can also be made by means of crimping or soldering to a lug 24.

From the foregoing description it will be obvious that the plate 16 performs three important functions; (l) the plate extension provides a mechanical and electrical anchor to the brush; (2) the plate rim makes a secure and low reistance Contact with the flexible conductor; and (3) a flat seat is provided for the expansion spring.

Having thus fully described the invention, what is claimed as new and desired to be secured by Letters Patent of the United States, is:

1. A carbon brush assembly for electrical circuits cornprising; a carbon brush rod for pressing against a moving electrical conductor, said rod mounted within a brush holder and formed with a cylindrical hole in one end thereof; a conductive metal plate mounted in contact with the brush and having a cylindrical extension for positioning within the hole in the brush; a helical spring also in the brush holder held between the plate and a portion of the holder for resiliently pressing the brush into contact with a movable portion of an electrical circuit; and securing means attached to the periphery of said metal plate for attachment to a flexible conductor.

2. An assembly as claimed in claim 1 wherein said extension is a force lit in said hole.

3. An assembly as claimed in claim 1 wherein said extension is formed with a plurality of axial corrugations on its outside surface for engagement with the inside surface of the hole to prevent relative rotation.

4. An assembly as claimed in claim 1 wherein a plurality of spaced spring tines are secured to the metal plate for resilient contact with the inside cylindrical surface of the hole.

5. An assembly as claimed in claim 1 wherein said metal plate includes a turned-over edge for crimping a flexible conductor into conductive contact therewith.

6. An assembly as claimed in claim 1 wherein the metal plate is formed with an outwardly extending lug for attachment to an electrical conductor.

7. An assembly as claimed in claim 6 wherein the lug is soldered to the conductor.

8. An assembly as claimed in claim 6 wherein the lug is formed with two flexible portions for crimping around a conductor.

References Cited UNITED STATES PATENTS 2,615,939 10/1952 Mitchell 310-247 3,028,515 4/ 1962 Cheetharn 310-247 3,339,098 8/1967 Burrows et al 310--247 3,376,444 4/ 1968 Eaton et al 310-247 MILTON O. HIRSHFIELD, Primary Examiner L. L. SMITH, Assistant Examiner U.S. Cl. X.R. 310-249 

